Conventionally, a backrest of a sofa is fixed on a sofa seat, as a result, the room defined by the backrest and the sofa seat and supplying for people seating is constant. Thus not every consumer with different ages may obtain a comfortable feeling when seating on such a sofa, due to their different physiques. In addition, this old sofa has only function for seating, which can not meet various demands of the consumers.
For improving the drawbacks mentioned above, some improved sofas for reclining or lying are developed. An adjuster is added to the sofa for adjusting angles and positions of the headrest or backrest, so that the using mode of the sofa could be changed.
In prior art, an adjuster for adjusting positions of the backrest is a linkage which has one end fixed on the backrest and the other end fixed on the sofa seat, so as to twist a parallelogram to move the backrest forwards or backwards. However, the linkage has some drawbacks as follows. First, due to the restriction of a parallelogram structure, the movement route during the adjusting of the backrest is an arc, but not a straight line (that is the movement is not a pure translation movement), which causes the adjusting to be inconvenient. Besides, the linkage must sustain the whole weight of the backrest, which may damage the backrest. Second, only two using positions (one forward and one backward) are provided to be adjusted, which also could not meet the demand of various using positions.
Therefore, it's a need to provide a backrest translation mechanism with multiple using positions for adjusting the translation movement of the backrest.